The present invention relates to a recording and reproducing apparatus for digital image information.
Digital image information has a huge amount of information. On the other hand, since communication capacity (memory capacity of a recording medium) of a transmission line used to transmit (record and reproduce) digital image information has a limitation, image information is compressed in the case where digital image information is transmitted (recorded and reproduced).
Representative examples of standards of the compression of image information include, for example, standards known as JPEG, MPEG 1, 2, and DVC standards known as standards of the compression of image information in digital VTR in which an interlaced scanning television signal is compressed, after which it is recorded.
Incidentally, the DVC standards are standards established as a result of discussion made in a "Discussion Meeting of HD Digital VCR" in which a number of VTR makers, research institutes and the like in many countries in the world are participated. In detail, the DVC standards are established with respect to the home digital VTR (VCR) in which a running magnetic tape is helically scanned by a rotary magnetic head, and digital data can be azimuth-recorded and reproduced on and from the magnetic tape.
In the DVC standards, the highly efficient image compression are carried out by various techniques such as discrete cosine transform (DCT), adaptive quantization, variable length coding and the like.
For example, with respect to the video signal of a so-called 525/60 system, suppose that the ratio of sampling frequency between a luminance signal Y, and chrominance signals Cb and Cr is 4:1:1. In this case, the number of effective pixels of the luminance signal in a horizontal direction is 720 and the number of effective lines in a vertical direction per frame is 480. Further, the number of effective pixels of the chrominance signals Cb and Cr in the horizontal direction is 180 and the number of effective lines in the vertical direction per frame is 480.
Further, with respect to the video signal of a so-called 625/50 system, suppose that the ratio of sampling frequency between a luminance signal Y, and chrominance signals Cb and Cr is 4:2:0. In this case, the number of effective pixels of the luminance signal in a horizontal direction is 720 and the number of effective lines in a vertical direction per frame is 576 and the number of effective pixels of the chrominance signals Cb and Cr is 360 and the number of effective lines in a vertical direction per frame is 288.
The effective pixel data in a moving picture signal to be recorded is divided per pixel block of a unit having a predetermined block size subjected to the orthogonal transform (the unit pixel block is a DCT block when the orthogonal transform is the discrete cosine transform). Each DCT block is subjected to the discrete cosine transform (DCT). The DCT block is constituted to have a block size of horizontal 8 pixels.times.vertical 8 pixels with respect to pixels within one frame for the luminance signal Y, and the chrominance signals Cb and Cr.
One frame for the moving picture signals to be recorded is divided per region (macro block) of a predetermined size in which one or more pixel blocks of the aforementioned unit are included.
The macro block is constituted as shown in FIG. 1A in the case where, with respect to the video signal of the so-called 525/60 system, the ratio of sampling frequency between a luminance signal Y, and chrominance signals Cb and Cr is 4:1:1. In detail, the macro block is composed of four DCT blocks DC0 to DC3 of the luminance signal, one DCT block DC4 of the chrominance signal Cb, and one DCT block DC5 of the chrominance signal Cr. These DCT blocks are obtained in the image region where one DCT block is obtained for the chrominance signal having a block size of horizontal 8 pixels.times.vertical 8 pixels.
Further, the macro block is composed as shown in FIG. 1B in the case where with respect to the video signal of the so-called 625/50 system, the ratio of sampling frequency between a luminance signal Y, and chrominance signals Cb and Cr is 4:2:0. In detail, the macro block is composed of four DCT blocks DC0 to DC3 by the luminance signal, one DCT block DC4 of the chrominance signal Cb and one DCT block DC5 of the chrominance signal Cr. These DCT blocks are also obtained in the image region where one DCT block of the chrominance signal having a block size of horizontal 8 pixels.times.vertical 8 pixels.
One image plane is divided by a super block composed of 27 macro blocks as a unit. In FIG. 2A, 50 divisions shown at (SO, 0), (SO, 1), (SO, 2) . . . , (S9, 2), (S9, 3), (S9, 4) are 50 super blocks composed in one frame. In FIGS. 2A and 2B, "i" designates the number of row and "j" designates the number of column. FIG. 2B shows the constitution of 5 super blocks (Si, j) set in one row per 27 macro blocks by taking any suitable one row in FIG. 2A.
FIGS. 3A and 3B show the super block for the 625/50 system. In FIG. 3A, 60 divisions shown at (SO, 0), (SO, 1), (SO, 2) . . . , (S11, 2), (S11, 3), (S11, 4) are 60 super blocks that constitute in one image plane. FIG. 3B shows a super block composed of 27 macro blocks.
In the DVC standards, one video segment is composed of 5 macro blocks which are obtained by, first, selecting one super block per column out of 10 super blocks belonging to each row in 50 super blocks (SO, 0), (30, 1), (S0, 2), . . . , (S9, 2), (S9, 3), (S9, 4) which constitute one image plane shown in FIG. 2A, and then taking out one macro block per super block selected as described above.
The control of data amount during the compression is carried out so that the data amount is within a predetermined amount in unit of one video segment.
Modes of DCT operation in the DVC standards include, with respect to the DCT block of horizontal 8 pixels.times.vertical 8 pixels, a mode for carrying out 8.times.8 DCT operation and another mode in which the 8.times.4 DCT operation is carried out with horizontal 8 pixels.times.vertical 4 pixels field by field, and the sum of and difference between the DCT coefficients are taken. The modes can be switched adaptively when coding.
The DCT coefficients obtained by the DCT operation are quantized with a quantization table that is selected so that the data amount after being applied with quantization and variable length coding is less than a predetermined value and closest to the predetermined value. In the quantization, the DCT blocks are divided into classes according to circumstances of the DCT blocks (such as a dispersion value of a pixel value in the DCT block), the quantization step is varied according to the classes to select one quantization table in macro block unit.
The data after variable length coding is subjected to formatting as shown in FIG. 4 when recorded on the magnetic tape. In FIG. 4, "QNO" indicates a quantization table number selected when compressed used as one of various parameters which is necessary when decoding together with data after variable length coding, "STA" information of error and concealment, "C" class information per DCT block and "M" mode information of the DCT operation.
All the information of one video segment are stored in 5 sync blocks. DC coefficients (DC components) of DCT coefficients in each of the DCT blocks DC0 to DC5 in the macro blocks shown in FIG. 1A are stored in a DC storage region in FIG. 4. Further, AC components of the DC coefficients are basically stored in an AC region in the same sync block as where the DC components are stored. However, in the case where the data amount is larger than the memory capacity of the storage region, they are stored in a vacant AC storage region in the sync block or another vacant AC storage region in the same video segment.
The formatted data are recorded in the magnetic tape in the form of a sync block constituted by adding parity words (inner parity) for SYNC word, ID code and error correction coding thereto, as shown in FIG. 5. Image data per frame is recorded by dividing it into 10 recording tracks. Image data per row shown in FIG. 2B is recorded in one recording track.
A track pair number indicating the sync block of which one of 10 recording tracks constituting image data per frame and a sync block number indicating which sync block in one recording track are recorded in the storage region of ID code in FIG. 5. Further, a sequence number (SEQ. No) in addition to these data is also stored in the ID code of the sync block in which image data is stored.
In the DVC standards, for the image signal according to the scanning standard of (2:1) interlaced scanning, highly-efficient coding is carried out only by intraframe coding. Further, since a motion vector is not used for highly-efficient compression, simple configurations can be achieved on a coding and a decoding apparatus, and editing operation can be easily carried out. Recently, there are manufactured VTRs for public use in which image data subjected to image information compression according to the DVC standards can be recorded and reproduced.
However, if there can be provided a recording and reproducing (transmission) apparatus capable of carrying out highly-efficient compression of image signal according to the scanning standard of sequential scanning of higher quality as compared with the image signal according to the scanning standard of (1:2) interlaced scanning as described above without addition of a considerable change in the constitution of apparatuses prepared in accordance with the DVC standards, such an apparatus can be effectively used for many applications and uses. Therefore, such an apparatus has been demanded.